Re: [PATCH v1 04/11] arm_mpam: Add missing mon_sel locking in MBWU restore

[Gavin Shan <gshan@redhat.com>]

On 7/10/26 9:55 PM, Ben Horgan wrote:
> The mon_sel_lock is used to protect the mbwu_state, as well as h/w accesses
> that use MPAMCFG_MON_SEL. However, in mpam_restore_mbwu_state() mbwu_state
> is accessed without holding the mon_sel_lock.
> 
> Add the missing locking.
> 
> Fixes: 41e8a14950e1 ("arm_mpam: Track bandwidth counter state for power management")
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
>   drivers/resctrl/mpam_devices.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 11b10c3bc334..b34e2a368516 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -1648,16 +1648,24 @@ static int mpam_restore_mbwu_state(void *_ris)
>   	u64 val;
>   	struct mon_read mwbu_arg;
>   	struct mpam_msc_ris *ris = _ris;
> +	struct mpam_msc *msc = ris->vmsc->msc;
>   	struct mpam_class *class = ris->vmsc->comp->class;
>   
>   	for (i = 0; i < ris->props.num_mbwu_mon; i++) {
> +		if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
> +			return -EIO;
> +

The code can be simplified by avoiding the unnecessary nested conditional statement,
something like below:

		if (!ris->mbwu_state[i].enabled) {
			mpam_mon_sel_unlock(msc);
			continue;
		}

		mwbu_arg.ris = ris;
                 mwbu_arg.ctx = &ris->mbwu_state[i].cfg;
		mwbu_arg.type = mpam_msmon_choose_counter(class);
		mwbu_arg.val = &val;

                 mpam_mon_sel_unlock(msc);

                 __ris_msmon_read(&mwbu_arg);

>   		if (ris->mbwu_state[i].enabled) {
>   			mwbu_arg.ris = ris;
>   			mwbu_arg.ctx = &ris->mbwu_state[i].cfg;
>   			mwbu_arg.type = mpam_msmon_choose_counter(class);
>   			mwbu_arg.val = &val;
>   
> +			mpam_mon_sel_unlock(msc);
> +
>   			__ris_msmon_read(&mwbu_arg);
> +		} else {
> +			mpam_mon_sel_unlock(msc);
>   		}
>   	}
>   

Thanks,
Gavin